Are you talking about l0li body always reverting to flat or adding a breast size bigger than size 4 (as there's 0-4 types)? If it's about l0li breast type there's a code in the Assembly-CSharp.dll which needs to be edited,
Surgy made a mod disabling that check for 1.2.10, I don't know if he did the same for newer Mono versions.
If it's about adding new breast size, I can basically duplicate a slot in a spine data, "breast type 4" for example, enlarge it a bit and name it "5" so all you'll have to do is to edit the code to "connect it" with a new character.